It is a known practice, in sheet feeders for sheet-fed printing presses or other sheet-processing machines, to provide arrangements for automated stack change. These may consist of rack-type structures, so-called remaining-stack carrying devices, which are provided with thrusting and lifting drives for the horizontal and vertical movement. Such so-called non-stop stack changers are suited, for example, during the printing of paper sheets, i.e. in machine running, to take over remainders of finished sheet stacks from, for example, a pallet with grooves, and to deposit them again on a new sheet stack subsequently installed in the sheet feeder. Known devices are distinguished by high constructive and assembly expenditure and require special constructions of the sheet feeders. Further, devices are used here, the remaining-stack carrying device of which have a rack engaging into the grooves of the pallet. This rack is to be removed in the joining of the remaining stack with the newly installed sheet stack as a whole between the two stack parts. This involves high drive forces and places very strong stresses on the sheets lying next to the section point. Furthermore, restraining means are to be provided which prevent a shifting of the stack parts, and, in the process, severely strain the stack edges. Furthermore, the operation of the sheet feeder itself is severely hindered or even rendered impossible. The sheet flow is difficult to control in the changing operation, so that waste sheets result again and again.
Devices have already been developed that partly avoid some of the disadvantages described.
Thus, from DE 3931710 C2 there is known a nonstop sheet feeder for sheet-fed rotary presses. It has a remaining-stack carrying device which is arranged underneath a conveyor table leading from the sheet feeder to the sheet-fed rotary press. The remaining-stack carrying device has a closed frame on which there are arranged nonstop rods which can be driven as piston rods of individual cylinders by means of a pressure medium and which are drivable into grooves of a pallet carrying a sheet stack. In the driven-in state, the nonstop rods lie on both sides of the frame and they are to be removed in succession out of the range of the sheet feeder. Nothing is said about the operating sequence. The control of the nonstop rods is very expensive and is not directly adaptable to the requirements of the stack changing operation.
A sheet feeder is known from DE 4 203 500 A1. It has, parallel to the sheet feeder, and allocated to this on the face side, an auxiliary stack-carrying device as an independent component. With this, over a common drive, individually drivable pointed bars are provided that are drivable in grooves of a pallet carrying a sheet stack. The drive system has individual chain drives that are coupleable onto the particular pointed bars. For the guidance and accessibility of the chain drives there are required special construction measures. The chain drives are unclamped constantly under a stand of a frame of their own and they completely block the space in from of the sheet feeder, so that the latter is not accessible. In the stack-changing process, the pointed bars in the joining of main stack and remaining stack are removed, first on the outside, then in the middle and last in the zone between the pointed bars already pulled from the stack zone, so that a gentle depositing of the remaining stack onto the sheet stack is produced. For this purpose the chain drives are coupled in an expensive manner onto the pointed bars such that the pointed bars can be driven only in common.